煤基质膨胀收缩对储层渗透率影响的新数学模型

New mathematical model of the influence of coal matrix swelling and shrinkage on reservoir permeability

煤层渗透率变化受多种因素制约,其中有效应力和煤吸附–解吸过程中煤基质的膨胀/收缩是两个主要因素。基于这两方面影响因素,采用体积不变原理和MATCHSTICK模型,提出新的预测渗透率变化的模型,有效回避了经典模型中使用不确定参数引起的渗透率模拟误差问题。研究结果表明,渗透率随煤层压力的变化存在3种理论模型,煤层气排采过程中,应尽可能使得渗透率变化曲线呈现下降缓慢、抬升稳定快速且增幅较大的趋势。最后,通过与经典的Palmer-Mansoori模型和Shi-Durucan模型的模拟对比,并利用现场实测数据进行验证,证明了本文推导模型的正确性和实用性。

Coal seam permeability variation is affected by many constraints,of which the effective stress andswelling-shrinkage of the coal matrix are the major factors in the process of coal adsorption and desorption.Inthese two aspects,according to the volume invariance principle and the MATCHSTICK model,it brought out a newmodel that predicts permeability variations and effectively avoids the permeability simulation error problem usinguncertain parameters in classic models.Research results show that the permeability changes with coal seam pressureconsists of3kinds of theory models.We should as far as possible make the permeability curves present thetrend of slow decline,stable and rapid increase during coalbed methane production.At last,it proved that the derivedmodel is correct and practical through the comparison with classic P&M model and S&D model simulationand validation of field test data.